The present invention relates to a chemical solution process for time-delayed destruction of hypochlorite. The solution disinfects, sterilizes, bleaches and cleans inanimate objects, surfaces, solutions and the like. The solution contains both thiosulfate and hypochlorite, preferably alkali metal or alkaline earth metal salts of hypochlorite, with the hypochlorite providing free chlorine for sterilization and disinfection until the thiosulfate consumes the hypochlorite.
Sodium, potassium, lithium, and calcium hypochlorites are well known for their disinfection and bleaching properties. The disinfecting properties are discussed in U.S. Pat. No. 3,717,580 to Echols et al., in Canadian Patent No. 1,087,955 to Sokol et al., in G.B. Patent No. 2.094,992 to Tanaka et al., and in U.S. Pat. No. 4,167,561 to Lamberti et al. wherein it is disclosed that the duration of exposure to hypochlorite solutions may be controlled by addition of certain chemical reducing agents to the hypochlorite solutions.
The use of citrates, malates and other hydroxycarboxylic acid reducing agents which react slowly with hypochlorite to destroy residual activity is disclosed in Echols et al. and Sokol et al. The addition of still other reducing agents to aqueous solutions either before or after the generation of hypochlorite in these solutions is disclosed in Tanaka et al. It is significant that Tanaka et al. place "alkali or alkaline metal salts of thiosulfuric acid such as sodium thiosulfate" in the category only appropriate for addition to hypochlorite after sterilization, consistent with prior art knowledge that thiosulfate is one of the agents know "to decompose or reduce the sodium hypochlorite to an innoxious state in extremely short time . . . " (Tanaka et al.). Lamberti et al, describe the use of a mixed solution containing an organic compound, alpha-hydroxy-beta sulfosuccinate and hypochlorite. With this mixture, the user can, at a desired time, lower the pH and heat the solution to substantially destroy the hypochlorite after a suitable disinfection interval.
Although Echols et al. describe a hypochlorite-containing solution which is self-inactivating, their system suffers from the expotential loss of hypochlorite activity during disinfection. This continuous loss of hypochlorite necessitates compensation with higher initial levels of hypochlorite than would otherwise be required if inactivation were time-delayed. A further disadvantage of the Echols et al. system for destroying hypochlorite is found in animal model studies which indicate that the reaction between hypochlorite and hydroxycarboxylic acids products physiologically irritating and perhaps toxic oxidation by-products thereby limiting the pharmaceutical usefulness of this process.
Although Lamberti et al. describe the advantages of a time-delayed system for the destruction of hypochlorite (maintaining a constant level of hypochlorite during disinfection), their mixed solution of hypochlorite and reducing agent must be heated and/or and pH-adjusted to destroy the hypochlorite. These usage steps may be inconvenient or even impossible to implement in many applications, eg. spraying or in processing large volumes.
Recently the use of sodium thiosulfate reducing agent was described in the rapid inactivation of residual hydrogen peroxide following disinfection (Ogunbiyi, Clinical & Experimental Optometry, 69.1: January 1986). This "post-disinfection" addition of thiosulfate is in agreement with its use by Tanaka et al and consistent with its high reactivity with strong oxidizing agents.
Prior to the present invention however, it was not appreciated that the reactivity of thiosulfate with hypochlorite could be appropriately reduced by increasing the pH of the mixture. Thus it was surprising to discover that a quantity of thiosulfate sufficient to destroy the hypochlorite in a disinfection or sterilization solution, could be initially combined in that hypochlorite-containing solution (prior to disinfection) and still permit the disinfection or sterilization process to occur. Furthermore, it was not appreciated that a pH-controllable autocatalytic oxidation of thiosulfate could be utilized to destroy hypochlorite following a time delay whose duration could be programmed by adjusting the original pH of the thiosulfate-hypochlorite mixture. It was also not appreciated that a narrow and defined range of thiosulfate:hypochlorite mole ratios constrain the above process. Finally it was not appreciated that a self-inactivating hypochlorite disinfection system, initiated at substantially alkaline pH, could be self-titrating to achieve a substantially neutral pH, by including in the reaction solution a chemical which, upon a pH decrease in the reaction solution, became a pH buffer.
The present process requires only the simple mixing of common inorganic chemicals, in proper proportions, at room temperature. This process, producing only simply non-toxic inorganic reaction products, is compatible with food and drug use.